JBL Authentics L8 (and probably JBL Authentics L16) are speaker systems with support for Optical, Spotify, Airplay, and some more. The problem is that they lack documented ways to change source and volume.
I figured out how to control a JBL Authentics L8 device. Instructions and a Node-RED implementation is available at jbl-authentics (github.com)
I am also wondering, if actual JBL speakers can be used as a Media Player e.g. via Music Assistant. Especially the JBL Authentics 500 and 200 seem interesting.